Friction dissipates energy and causes wear resulting in damage to the equipment. The way to ensure that frictional effects are minimized is through proper lubrication. In carrying out this function, lubricants create a lubricant film on surfaces of moving parts. Lubricant additives can be used in automobiles, lubricants, greases, metal working fluids, oil and gas drilling, heavy machinery and other related industries.
The type of drilling fluids chosen for a given drilling operation depends on the formation being drilled, the depth, the mechanical resistance, and the pressure of the wellbore. Regardless of their type, drilling fluids maintain hole integrity, remove cuttings from the hole, prevent formation damage, suspend cuttings and weighting materials when circulation is stopped, cake off the permeable formation by preventing the passage of fluid into the formation, and cool down and lubricate the drill bit.
Even if a drilling fluid successfully meets all of the above requirements, there is no guarantee that the rate of penetration will be acceptable, since poor lubricity and high friction and drag increase pipe sticking and drilling cycle. The need to overcoming frictional forces is very much encountered during all stages of wells construction; including drilling, completion and maintenance, which originates from the rotation and/or sliding of a pipe inside the well in contact with either the wellbore (metal-to-rock) or the casing (metal-to-metal). These forces hinder directional and extended reach drilling by creating excessive torque and drag. Excessive torque and drag in highly directional and extended-reach wells can exceed the mechanical limits of the drilling equipment, which may expedite wear and tear of down hole tools and equipment and thereby limit production. These problems can be minimized by using drilling fluid with high capabilities of lubricating the different components.
Historically, oil-based products have been used as lubricants for the drilling operations. However, recent environmental regulations limit the usage of aromatic-based oil and require the adaptation of mineral oil, synthetic oil and water based mud where lubricant additives are found useful to increase the lubricity (Riley et al., 2012; Kercheville et al. 1986). In these instances, lubrication is achieved using additives such as liquid lubricants, including glycols, oils, esters, fatty acid esters, surfactants and polymer-based lubricants; and solid lubricants, such as graphite, calcium carbonate flakes, glass and plastic beads (Hoskins, 2010; Skalle et al., 1999). The main function of these additives is to lubricate the drill string and prevent differential sticking. But these available lubricants have not proven entirely effective and suffer from different disadvantages. Both liquid and large sized solid lubricants can cause permanent damage to the formation (Hoskins, 2010; Skalle et al., 1999; Lammons, 1984). Furthermore, micro and macro sized solid lubricants can interfere with drilling equipment and hinder production. The abrasive nature of macro and/or micro sized solid lubricants may cause higher kinetic energy and accelerate or aggravate the wear and tear of the downhole equipment (Amanullah et al., 2011). Some of these solids, nevertheless, get filtered out in the solids control equipment due to their large size and are, therefore, less problematic. Liquid lubricants can also negatively impact the physical and chemical properties of the drilling fluid and lead to foaming (Hoskins, 2010). To counter foaming, costly defoamers must be added to the system. Liquid lubricants form a film between two surfaces and, hence, minimize frequent contact and consequently friction. However, their efficiency largely depends on mud type and may depreciate in the presence of other types of mud additives. It should also be noted that the efficiency of liquid lubricants is entirely lost in high-solids muds. Solid lubricants, on the other hand, do not depreciate as much in such muds (Hoskins, 2010; Skalle et al., 1999). However, these materials are not sufficiently effective to serve their primary goals of reducing the coefficient of friction.
By virtue of their very small sizes, nanoparticles (NPs) have the potential of acting as effective lubricant additives. Their size and shape enable them to enter contact zones between surfaces easily. Inorganic nanoparticles mostly do not display any affinity to oil and may not be affected by the mud type. In-situ and ex-situ techniques for forming a wide variety of well dispersed NPs in an invert emulsion as well as water-based drilling fluid have been detailed in the art (Husein et al., 2012). These methods rely heavily on high shearing, which produces finely dispersed water pools, in the case of invert emulsion drilling fluids, and the use of these water pools as nanoreactors to form NPs with sizes mainly below 100 nm. Once formed, these NPs display very high stability in the mother drilling fluid and interact very effectively with the rest of the drilling fluid (Husein et al., 2012). Previous experiments showed that these particles perfectly seal filter cakes by creating crack-free, very smooth surfaces (Husein et al., 2012). Therefore, these particles contribute to the formation of slippery layers between the borehole and the drill string leading to lower overall friction coefficient and, subsequently, increase the extended reach of horizontal drilling. Moreover, due to the small sizes of these particles, the wear and tear of down hole equipment and tools becomes negligible as less kinetic energy (nano sized particles achieve lower sedimentation speed compare to the large sized particles) and abrasive action is encountered. Overall, the application of nanoparticles in drilling fluid presents a good potential for reducing friction while drilling and, hence, improve the extended reach.
Nanoparticles and nano-emulsion particularly have previously been used in drilling fluids and hydrocarbons for a variety of purposes.
U.S. Patent 20080234149 A1 (2008) is directed to a nanoparticles-based lubricant composed of solid lubricant nano-material (material selected from molybdenum disulphide, tungsten disulphide, gold, silver, lead and tin) having a size less than or equal to 500 nm and a second material which is a chemical surface active agent placed on an external surface of the nanoparticles to minimize particles agglomeration. The nanoparticle preparation protocol is not straight forward and involves many steps, which makes the approach commercially unattractive. This patent does not describe the use of the product particles in drilling fluids, and does not refer to the use of ferric hydroxide and calcium carbonate nanoparticles.
U.S. Pat. No. 6,710,020 (2004) discloses the application of hollow-inorganic fullerene (IF) nanoparticles as a lubricating additive for automotive transport applications. IF nanoparticles having diameters between 10 and 200 nm are slowly released to the surface from its base metal to provide lubrication. These nano-materials are synthesized in a fluidized bed reactor at 850° C. and require different cleaning and purification steps before they could be used. This technique of nanoparticle preparation produces particles with high surface activity, which tends to bind the particles together and limits the quantity of nanoparticles produced. This patent does not include measurements of friction coefficient of drilling fluids.
U.S. Patent 2011/162845 discloses a method of servicing a wellbore. It introduces a lost circulation composition into a lost circulation zone to reduce the loss of fluid into the formation. The lost circulation composition comprises Portland cement in an amount of about 10 wt % to about 20 wt % of the lost circulation composition, 1 to 100 nm nano-silica of 0.5 wt % to 4 wt %, 5 wt % to 10 wt % amorphous silica, 0.5 wt % to 2 wt % synthetic clay, 15 wt % to 50 wt % sub-micron sized calcium carbonate and 60 wt % to 75 wt % water. The lost circulation compositions rapidly developed static gel strength and remained pumpable for at least about 1 day. The sample was observed to gel while static but returned to liquid upon application of shear. This patent only shows the effectiveness in terms of lost circulation control by nano-materials and does not provide any data on friction coefficient of the drilling fluid.
U.S. Patent Application 2009/82230 (2009) relates to an aqueous-based well treatment fluid, including drilling fluids, containing a viscosifying additive. The additive has calcium carbonate nanoparticles with a median particle size of less than or equal to 1 μm. The amount of calcium carbonate nanoparticles used in the drilling fluid is approximately 20 wt %. The nanoparticles used in the well treatment fluid were capable of being suspended in the fluid without the aid of a polymeric viscosifying agent. The addition of nanoparticles altered the viscosity of the fluid. Nanoparticles suspended in a well treatment fluid exhibited sagging (inadequate suspension properties) particularly at high temperatures of around 350° F. The viscosity changes of a fluid upon addition of nanoparticles were well reported. However, even with the high amount of nanoparticles added to the fluid formulation, no fluid loss and lubricity data were reported.
U.S. Pat. No. 8,071,510 (2011) is directed to a method of increasing the lubricity or reducing the coefficient of friction of a drilling or completion fluid by using brine of at least one water soluble salt, vegetable oil and an anionic or non-ionic surfactant in order to assist in the solubilization of the salt. This patent does not describe the use of the nanoparticles for reducing the coefficient of friction. Further, the present inventors have found that sodium salts have a negative impact on lubricity quality, as set out below.
Yang et al. (2012) developed a nanoscale emulsion lubricating material to solve the high friction drag in drilling operation. It increased lubricity by 50 wt %, but did not improve fluid loss and viscosity property. Their work did not involve nanoparticles.
Riley et al. (2012) studied the addition of silica-based nanoparticles in drilling fluid and reported 20% lower coefficient of friction upon applying 150 lb/lbs of torque.
Other references, such as Amanullah et al. 2011, consider the use of small amounts of nanoparticles in water and indicate the potential for beneficial effects on differential sticking, torque reduction and reduction of drag problems in certain types of drilling. However, these references experiment with nanoparticles in water and require very active stabilizers to maintain the nanoparticle dispersions or look at the interaction of nanoparticles with other components that may be present in a well fluid. The references do not provide data directly relevant to lubricity results in industrial drilling fluids but merely indicate further areas for research.
It is, therefore, desirable to provide an improved drilling fluid having a decreased coefficient of friction.